An instrument illumination device for a vehicle, such as that as illustrated in FIG. 8, has been known (see, for example, Japanese Patent Application Laid-Open Publication No. 2010-139296).
This type of instrument illumination device is provided, inside a housing 2 of a vehicle instrument device 1, with a circuit board 3 that is made of synthetic resin as illustrated in FIG. 9.
To an inner face 3a of the circuit board 3, a small substrate 3b in the form of a small piece is fixedly attached opposite to an end face 4a of a light guide plate 4 of an arcuate shape, as illustrated in FIG. 8.
The small substrate 3b has an LED 5 mounted thereon for serving as a light source of the illumination light to enter the light guide plate 4. When the LED 5 is activated, the illumination light substantially entirely enters the end faces 4a of the light guide plate 4.
The function of such a conventional instrument illumination device will be described below.
In the conventional instrument illumination device configured as described above, as illustrated in FIG. 8 or FIG. 9, the illumination light from the LED 5 having entered the end face 4a of the light guide plate 4 is reflected within the light guide plate 4 and dispersed along a circumferential direction to illuminate a dial plate 16 from a rear side thereof in a main illumination area “a” illustrated in FIG. 9.
On this occasion, having high directionality, the illumination light of the LED 5 substantially entirely enters the light guide plate 4 from the end faces 4a and thereby an area “b” of the dial plate 16 immediately above the LED 5 is illuminated by a backlight.
However, in such a conventional instrument illumination device, depending upon the ornamental design of the dial plate, there may be an instance wherein not only the area “b” immediately above the LED 5, but also other area, such as an auxiliary illumination area “c” of an auxiliary instrument, for example, requires homogeneous illumination light as is the case with the main illumination area 1.